iMX6 Local Alpha

We are using local alpha (not in pixel but in a separate buffer) to combine a graphic plane and a video plane in kernel 4.1.15. Everything works fine except whenever turning local alpha on or off via ioctl MXCFB_SET_LOC_ALPHA, the screen flashes. We tracked this down to mxc_ipuv3_fb.c where the ioctl is handled. It seems this ioctl will always call the function mxcfb_set_par(). This function basically does a full reinit of fb0 and fb1 and causes the flashing. Turning global alpha on and off does not have such an issue. Isn't there a cleaner way to turn on local alpha?